Apparatus for controlled etching of metal



Jan. 1, 1963 M. s. HOWETH APPARATUS FOR CONTROLLED ETCHING OF METAL Filed Dec. 31, 1958 2 Sheets-Sheet l m m m m M42 mu 5 HOWE TH A T TOEME Y Jan. 1, 1963 V M. s. HOWETH 9 9 APPARATUS FOR CONTROLLED ETCHING OF METAL Filed Dec. 51, 1958 2 Sheets-Sheet 2 JNVENTOR. MAQV/M i HOWETH BY ATTOEL/EY ilnitc Fatented Jan. 1, i963 The present invention relates generally to metal reduction; more particularly it relates to the dimensional reduction of metal objects by controlled chemical action.

In recent years the complexity of aircraft configurational design has increased to the extent that it has become necessary to evolve and develop new manufacturing techniques for the fabrication of the components of such designs. For example advanced aircraft employ large contoured wing panels of a sandwich type construction. (Joe of the elements of such a panel is an external skin which is fabricated from a solid metal plate of which the thicknesses of certain areas are reduced in order to permit the placement of cellular type core material therein. Such skin is integrally reinforced and stiffened by the unreduced areas between suct reduced areas.

A structure of this character is extremely difficult to fabricate by conventional mechanical machining methods. if the curvature of the skin is formed after the areas have been reduced, undesirable deformation very often results in these areas. if the curvature is formed before the at as are reduced, such reduction is very difficult and expensive.

By utilizing chemical action, however, it is relatively easy and comparatively simple to fabricate such a structure. A plate, the thickness of which is equal to the thickness of the unreduced areas, is first formed to the desired curvature. The stiffening areas are next masked with a suitably chemically inert synthetic material. The metal of the unmasked areas is then subjected to the action of a chemical agent which reacts with such metal and reduces the thickness thereof to the desired dimension.

lcretofore the chemical reduction of metal workpieces has been accomplished by immersing a plate or workpieces in a suitable etchant solution contained within a tank. When the workpiece has been immersed for a period of time sullicient to yield the desired depth of etch, it is removed from the first tank containing the etchant solution and immersed in a second tank containing water, such water immersion terminating the etch reaction. After the usual etch operations the workpiece is covered by an undesirable, black residue or smut," which necessitates the immersion of the workpiece in a third tank containing a brightening or desmutting agent.

Several disadvantages are inherent in such etching apparatus. The etch-rate or rate-of-removal of metal is comparatively low, on the order of .001 inch per minute. Moreover, continued use of the etchant solution results in the contamination thereof by a precipitate formed of the removed metallic cations and the anions present in the etchant solution; such contamination further reducing the effectiveness of the solution and resulting in a continually diminishing etch-rate. Eventually, when the etchaut solution reaches a certain contamination level, etching operations must be suspended and the contaminated solution replaced, which is both time consuming and expensive. Another serious disadvantage is that the tanks containing the various solutions are generally large and require an excessive amount of manufacturing floor space.

The present invention comprises an apparatus for the controlled chemical corrosion of metal workpieces wherein the corrosion solution is applied thereto in vapor form within an atmosphere, the temperature and pressure of which are controlled at their optimum values.

The present invention offers several advantages over previous etching devices. The metal removal rate of this apparatus is much greater than prior devices, thereby making the operation more economical. Moreover, there is no contamination of the corrosion solution; hence the rate of removal of the metal is constant. This invention is further advantageous in that corrosion agent, corrosion agent concentration, pressure and temperature may be controlled and varied to suit the metal or alloy to be corroded in a particular operation. The present apparatus in addition to the metal removal operation also lends itself to such associated operations as degreasing, rinsing and brightening, all of which may be accomplished in a single container. And, since a single container is employed, the manufacturing floor space required is substantially less than that previously required for operations of this type.

it is, therefore, an object of the present invention to provide an apparatus for the useful, controlled corrosion of metal objects wherein such metal objects are exposed to the chemical action of a corrosive soltuion in vapor form within an atmosphere wherein the pressure and temperature are controlled at their optimum values.

Another object resides in the provision of an apparatus for the controlled corrosion of metal workpieces, such apparatus affording a greater rate of removal of metal from such workpieces than heretofore possible.

Yet another object is to provide an apparatus for the useful and controlled corrosion of metal objects which is economical in operation.

Still another object of the invention is to provide an apparatus for corrosion of metal workpieces at a constant rate.

A further object resides in the provision of an apparatus for the controlled corrosion of metal objects which is also adapted to perform such associated operations as degreasing, cleaning, rinsing and brightening.

A still further object is to provide an apparatus for the corrosion of metal objects of various composition, such apparatus including means for varying the corrosion agent composition, the corrosion agent concentration, and the temperature and pressure of the atmosphere surrounding such metal objects.

These and other objects and advantages will be more apparent to those skilled in the art from the following description of the appended drawings wherein:

FlGURE 1 is a perspective view of the preferred embodiment of the invention; and

FIGURE 2 shows the apparatus of FIGURE 1 in crosssection.

The present invention comprises four basic components: A receptacle having a chamber therewithin wherein is contained the workpiece to be corroded, a corrosion agent supply system for injecting such corrosion agent into such chamber, a pressurization system for pressurizing such chamber, and a calefaction system for heating such chamber.

Referring now to the drawings, the autoclave receptacle, generally indicated by the numeral 10, is of a substantially cylindrical configuration, open at one end in order to receive the workholding device 11 therein; which device in turn, supports, in vertical position, a workpiece 12. The open end of autoclave it? is provided with a door 13, hinged at 14, the closure of which effects an airtight seal of the autoclave receptacle. Blocks 15 serve to fixedly support the receptacle 10.

The receptacle ltl (FIGURE 2) comprises two concentric, cylindrical members, an outer cylinder 16 and an inner cylinder 17.

The inner cylinder 17 is supported within outer cylinder 16 by means of spacer blocks 18 therebetween. Such concentric cylinders 16 and 17 divide the interior of the receptacle into two chambers, a central chamber 1? de fined by inner cylinder 17, and a peripheral chamber 21 intermediate cylnders 16 and 17. It is to be noted that such chambers are entirely distinct and separate, each from the other. The external cylinder 16 is inclosed within a layer of suitable insulating material 21 which serves the purpose of safety as Well as to minimize heat loss to the ambient atmosphere. A drainpipe 22, the purpose and function of which will be explained hereinafter, enters internal cylinder 17 at the lowermost position thereof.

Along the lower surface of inner cylinder 17 there are positioned a pair of step ledges 23, which extend sub stantially the length of receptacle lttl and which serve to support rails 24. The top surfaces of such rails 24 are of convex curvature, such as will conform to the concave surfaces of Wheels 25 of Workholding device 11. inasmuch as many of the workpieces to be fabricated by means of the present apparatus are of considerable size and wei ht (of the order of several hundred pounds), it is desirable that a track of rails, similar to those described, be provided external to the apparatus so that the work piece 12 may be loaded into the workholding device 11 while such device remains on the track, and the workholding device then rolled into the chamber 19. A laterally movable track section is provided immediately adjacent the opening of receptacle in order to permit closure of door 13.

The corrosive agent supply system comprises a plurality of feeder lines 27 (FIGURE 1) from a corresponding number of suitable storage tanks (not shown). The storage tanks are provided with pumps so that the corrosive solutions are delivered under pressure. The invention anticipates the use of caustic and acidic corrosive agents, degreasing agents such as trichloroethylene, desmutting or brightening agents such as a low concentration mixture of nitric and hydrofluoric acid, and water which is utilized to terminate all chemical reactions and to rinse the workpieces.

Feeder lines 27 enter the control console unit 28, to be described in greater detail hereinafter, wherein are disposed a plurality of valves, the number of which is equal to the number of feeder lines. The opening and closing of such valves are effected by means of hand wheels 29 which extend through the forward face of console unit 28. Each of the valves communicate with a manifold 36. Such manifold 39, in turn, communicates with one of the longitudinal conduit manifolds 31 as indicated at 32 (FlGURE 2). Such longitudinal manifolds 31 (FIG- URE l) are spaced about the external surface of receptacle it) and extend substantially the length thereof. Near the aft end of the receptacle ill a transverse, circumferential conduit 33 joins the longitudinal manifolds 31. At spaced intervals along longitudinal manifolds 31 inwardly directed radial members 34 extend through receptacle lltl into central chamber 19 (FIGURE 2). Vaporizer nozzles 35 are affixed to the ends of such extensions 34, such nozzles serving to vaporize the corrosive agent as it enters the chamber 19. Sealing glands 36 serve to effect an airtight seal between radial members 34 and inner cylinder 17.

The pressurization of the central chamber 19 is effected by means of a suitable, conventional air compressor unit 38 (FIGURE 1). A cylindrical pressure reservoir tank 39 initially accepts the compressed air from compressor unit 38. From the reservoir tank 39 the compressed air is admitted into central chamber 1% (FIGURE 1) through the pressure conduit 43.

The desired pressure is maintained within central chamber 1? by means of a pressure relief-filter mechanism 41 which may be set to the desired pressure by means of handle 42. Such pressure relief-filter mechanism communicates with central chamber 19 through conduit @3. Should the pressure in chamber 19 become higher than the desired pressure, the valve of the pressure relief-filter device opens and some of the vapor enters the filter where such vapor is reacted with a suitable chemical agent thus transforming it into a harmless compound, which then exits through exhaust conduit 44 to the surrounding atmosphere, thereby reducing the pressure of chamber 19.

The temperature of central chamber 19 is raised by means of circulating superheated steam from a suitable earn generator (not shown) through peripheral chamer 20. The steam is admitted thereto through a steam onduit A drain pipe 46 at the lowest point of exernal cylinder 16 is provided for draining off the condensed steam. An adjustable thermostat 4'7 (FIGURE 1) maintains he desired temperature within the chamber 19 (FIGURE 2) by controlling the output of the steam generator. in the event that a low temperature is desired, a suitable refrigerant gas may be circulated in peripheral chamber Ztl.

The console control unit 23 (FIGURE 1), in addition to housing the feeder line valves as described above, also encases a pair of pyrometers 43 which indicate the temperature within chamber 19, a row of pressure gauges '29 which indicate the air pressure at representative positions within chamber 19, and a row of feeder line pressure gauges 59 which indicate the pressures in the respective feeder lines 27.

it is to be understood that the surfaces of those elements of the invention which would be exposed to the corrosive solutions are protected by coatings of such chemical nature as will successfully resist corrosion from such solutions. in general it is desirable to line or cover exposed surfaces with a chemically inert, synthetic material such as an unplasticised polyvinyl compound of which the commercially available Teflon and Kel-F are examples, In some instances, howe er, it may be more practicable to utilize a plurality of separate manifold systems, each of which is fabricated of a metal which resists or inhibits corrosion by the particular corrosion agent to be circulated therethrough.

The preparation of an object, such as the workpiece 12, for the controlled corrosion thereof, involves the steps of rigorously cleaning the object and masking certain areas thereof with a suitable inhibitive substance, unreactive with the corrosive agent to he used, in order to prevent the corrosion of such areas.

Cleaning is normally accomplished by first manually wiping the object with a cloth dampened with a suitable solvent such as methyl ethyl ketone. The workpiece is then placed in a workholding device 11 and enclosed within central chamber 19 of autoclave receptacle 19. When the appropriate temperature and pressure have been obtained, a degreasing agent, for example trichloroethylene, is injected in vapor form into the chamber 19. When the object has been degreased for a predetermined time, a clenaing agent, such as a very mild solution of nitric and hydrofluoric acids, is similarly applied thereto. The object is then rinsed with water vapor, removed from the receptacle and allowed to dry.

The masking substance is next applied to the surface of the object. The areas to be reduced or corroded away, as indicated at 51 (FEGURE l), are trimmed and re moved from the workpiece 12 leaving areas 52 covered by the masking substance. in the example shown, the workpiece 12 is a plate, whereby it is desired to reduce the thickness of the unmasked areas 51 a predetermined amount, leaving the masked areas 51 intact.

When the workpiece 12 has been cleaned and masked as described above, it is ready to be corroded in a precisely controlled manner. in the actual corrosion operation, as in the degreasiug and cleaning operations referred to previously, the workpiece i2 is sealably enclosed Within the central chamber 19 of receptacle it The desired temperature and pressure are set on thermostat 47 and pressure relief-filter device il respectively and the operation of the heating and pressurization systems is initiated. The operation of the pressure pump for the corrosive agent to be employed is also initiated. When the required temperature and pressures have been obtained, as indicated by pyrometers 48, chamber pressure gauges 49 and the appropriate feeder line pressure gauge 50, the valve within control console unit 23 which corresponds to the feeder line supplying the corrosive agent to be used is opened by means of the proper handwheel 29, thus allowing the corrosive agent to flow through manifolds 3t) and 31, conduit 33, radial members 34 and nozzles 35. The corrosive agent is vaporized by nozzles 35 as it enters the central chamber 19. There is thus effected within the central chamber 19 and about the workpiece 12, an atmosphere of which the chemical composition, cencentration, temperature, and pressure are controlled at their optimum values. The workpiece 12 is subjected to the chemical action of the corrosive agent for a predetermined time, such time being determined by dividing the desired depth of metal removal in areas 51 by the known rate of removal of the particular corrosive agent under the prevailing conditions of pressure and temperature.

As the corrosive agent reacts with the metal of the workpiece, a liquid precipitate is formed which collects at the bottom of the chamber 19 Such precipitate is drained off through drainpipe 22 (FIGURE 2).

When the required time has elapsed, the corrosive agent supply valve is closed and the water line valve is opened, and water vapor is injected into chamber 19, thereby terminating the corrosion reaction and rinsing the workpiece. If necessary the workpiece is similarly subjected to the action of a brightening agent after which it is again rinsed with water vapor. The operation of the heating and pressurization systems are then terminated, and the pressure withinthe chamber 19 released by opening the valve of pressure relief-filter device 41.

The workpiece l2 and workholding device 11 are thereupon removed from the receptacle 10. When it has cooled sufficiently, the workpiece 12 is removed from the workholding device ill, stripped of masking material and, if necessary, trimmed to desired size. This having been accomplished, the workpiece is now ready for its intended end use.

As thus described the present invention resides in a novel, efiicient and economical device for performing operations on metal objects wherein it is desired to precisely reduce certain dimensions of such objects; such device comprising, in combination, a receptacle defining a chamber wherein is placed the metal object to be reduced, means for delivering to such chamber a vaporized corrosion solution, means for controlling the pressure of such chamber, and means for controlling the temperature of such chamber.

Although only the preferred embodiment of the invention has been herein disclosed, it is to be understood that the invention is not limited thereto, as many modifications and variations will be apparent to those skilled in the art, and the invention is to be given the broadest possible interpretation within the terms of the following claims.

I claim:

1. Apparatus for controlled chemical corrosion of metal workpieces comprising a receptacle for receiving said workpieces, a corrosion agent supply system for supplying said receptacle with corrosion agents, a pressurization system for pressurizing said receptacle and a temperature control system to regulate temperature within said receptacle whereby said workpieces may be corroded to remove metal from selected portions thereof under controlled conditions of agent concentration, pressure and temperature, said receptacle including an inner cylindrical member defining a central chamber, an outer cylindrical member around said inner member to define a peripheral chamber, and a workholding device for holding a workpiece in position in said central chamber for exposure to said corrosion agents, said corrosion agent supply system including a plurality of feeder lines communicable with separate sources of pressurized fluid and extending from said sources to said receptacle, inwardly directed radial members extending through said receptacle and having vaporizer nozzles thereon positioned within said central chamber, and valves in said feeder lines for selectively releasing fluid from certain of said sources to said receptacle, said pressurization system including conduit means in communication with said central chamber for pressurizing said central chamber to a predetermined value, pressure relief means to provide for the escape of gases and vapor from said central chamber including a suitable filter mechanism to render said escaping gases and vapors harmless, and an exhaust conduit to permit passage of said gases and vapors under pressure, said temperature control system including means for circulating superheated steam in said peripheral chamber and a suitable drain at the bottom thereof to drain condensed steam vapor.

2. Apparatus for controlled chemical corrosion of metal workpieces comprising a receptacle for receiving said workpieces, a corrosion agent supply system for supplying said receptacle with corrosion agents, a pres surization system for pressurizing said receptacle and a temperature control system to regulate temperature within said receptacle whereby said workpieces may be corroded to remove metal from selected portions thereof under controlled conditions of agent concentration, pressure and temperature, said receptacle including an inner cylindrical member defining a central chamber, an outer cylindrical member around said inner member to define a peripheral chamber, and a workholding device for holding said workpieces in position in said central chamber for exposure to said corrosion agents, said corrosion agent supply system including a plurality of feeder lines communicable at one end with sources of fluid under pressure and at the other end with means for conducting said fluid interiorly of said receptacle and for vaporizing the fluid therein to effectively expose said workpiece to the fluid, and valves interposed in said corrosion agent supply system to selectively control the flow of said fluid from said sources into said receptacle, said pressurization system including conduit means in communication with said central chamber for prcssurizing said central chamber to a predetermined value, pressure relief means to provide for the escape of gases and vapor from said central chamber including a suitable filter mechanism to render said escaping gases and vapors harmless, and an exhaust conduit to permit passage of said gases and vapors under pressure, said temperature control system including means positioned in said peripheral chamber for effecting the temperature condition within said receptacle.

3. Apparatus for controlled chemical corrosion of metal workpieces comprising a receptacle for receiving said workpieces, a corrosion agent supply system for supplying said rcceptacle with corrosion agents, a pressurization system for pressurizing said receptacle and a temperature control system to regulate temperature within said receptacle whereby said workpieces may be corroded to remove metal from selected portions thereof under controlled conditions of agent concentration, pressure and temperature, said receptacle including an inner cylindrical member defining a central chamber, an outer cylindrical member around said inner member to define a peripheral chamber, and a workholding device for holding said workpieces in position in said central chamber for exposure to said corrosion agents, said corrosion agent supply system including means for selectively feeding fluids under pressure into said receptacle and for vaporizing said fluids to effectively expose said workpiece to same, said pressurization system including conduit means in communication with said central chamber for pressurizing said central chamber to a predetermined value, pressure relief means to provide for the escape of gases and vapor from said central chamber including a suitable filter mechanism to render said escaping gases and vapors harmless, and an exhaust conduit to permit passage of said gases and vapors under pressure, said temperature control system including means acting within said peripheral chamber to bring about the tempera ture condition desired Within said receptacle.

4. Apparatus for controlled chemical corrosion of metal workpieces comprising a receptacle for receiving said W rkpleces, a corrosion agent supply system for supplying said receptacle with corrosion agents, a pressurization system for pressurizing said receptacle and a temperature control system to regulate temperature Within said receptacle whereby said workpieces may be corroded to remove metal from selected portions thereof under controlled conditions of agent concentration, pressure and temperature, said receptacle including an inner cylindrical member defining a central chamber, an outer cylindrical member around said inner member to define a peripheral chamber, and a workholding device for holding said workpieces in a generally upright position in said central chamber, said corrosion agent supply system including a plurality of feeder lines communicable with separate sources of pressurized fluid and extending from said sources to said receptacle, inwardly directed radial members communicating with said feeder lines and extending through said receptacle and having vaporizer nozzles thereon positioned within said central chamber, and valves in said feeder lines for selectively releasing fluid from certain of said sources to said receptacle, said pressurization system including conduit means in communication with said central chamber for pressurizing said central chamber to a predetermined value, pressure relief means to provide for the escape of gases and vapor from said central chamber including a suitable filter mechanism to render said escaping gases and vapors harmless, and an exhaust conduit to permit passage of said gases and vapors under pressure, said temperature control system including means for circulating superheated steam in said peripheral chamber and a suitable drain at the bottom tnereof to drain condensed steam vapor.

References Cited in the tile of this patent UNITED STATES PATENTS 

1. APPARATUS FOR CONTROLLED CHEMICAL CORROSION OF METAL WORKPIECES COMPRISING A RECEPTACLE FOR RECEIVING SAID WORKPIECES, A CORROSION AGENT SUPPLY SYSTEM FOR SUPPLYING SAID RECEPTACLE WITH CORROSION AGENTS, A PRESSURIZATION SYSTEM FOR PRESSURIZING SAID RECEPTACLE AND A TEMPERATURE CONTROL SYSTEM TO REGULATE TEMPERATURE WITHIN SAID RECEPTACLE WHEREBY SAID WORKPIECES MAY BE CORRODED TO REMOVE METAL FROM SELECTED PORTIONS THEREOF UNDER CONTROLLED CONDITIONS OF AGENT CONCENTRATION, PRESSURE AND TEMPERATURE, SAID RECEPTACLE INCLUDING AN INNER CYLINDRICAL MEMBER DEFINING A CENTRAL CHAMBER, AN OUTER CYLINDRICAL MEMBER AROUND SAID INNER MEMBER TO DEFINE A PERIPHERAL CHAMBER, AND A WORKHOLDING DEVICE FOR HOLDING A WORKPIECE IN POSITION IN SAID CENTRAL CHAMBER FOR EXPOSURE TO SAID CORROSION AGENTS, SAID CORROSION AGENT SUPPLY SYSTEM INCLUDING A PLURALITY OF FEEDER LINES COMMUNICABLE WITH SEPARATE SOURCES OF PRESSURIZED FLUID AND EXTENDING FROM SAID SOURCES TO SAID RECEPTACLE, INWARDLY DIRECTED RADIAL MEMBERS EXTENDING THROUGH SAID RECEPTACLE AND HAVING VAPORIZER NOZZLES THEREON POSITIONED WITHIN SAID CENTRAL CHAMBER, AND VALVES IN SAID FEEDER LINES FOR SELECTIVELY RELEASING FLUID FROM CERTAIN OF SAID SOURCES TO SAID RECEPTACLE, SAID PRESSURIZATION SYSTEM INCLUDING CONDUIT MEANS IN COMMUNICATION WITH SAID CENTRAL CHAMBER FOR PRESSURIZING SAID CENTRAL CHAMBER TO A PREDETERMINED VALUE, PRESSURE RELIEF MEANS TO PROVIDE FOR THE ESCAPE OF GASES AND VAPOR FROM SAID CENTRAL CHAMBER INCLUDING A SUITABLE FILTER MECHANISM TO RENDER SAID ESCAPING GASES AND VAPORS HARMLESS, AND AN EXHAUST CONDUIT TO PERMIT PASSAGE OF SAID GASES AND VAPORS UNDER PRESSURE, SAID TEMPERATURE CONTROL SYSTEM INCLUDING MEANS FOR CIRCULATING SUPERHEATED STEAM IN SAID PERIPHERAL CHAMBER AND A SUITABLE DRAIN AT THE BOTTOM THEREOF TO DRAIN CONDENSED STEAM VAPOR. 